Re: [PATCH v4 15/59] struct filename: saner handling of long names

Al Viro
2026-01-13T19:15:38Z

On Tue, Jan 13, 2026 at 07:07:01PM +0000, Al Viro wrote:

> FWIW, an unpleasant surprise is that LTP apparently doesn't test that
> case anywhere - the effect of that braino is to lower the cutoff for
> name length by 48 characters and there's not a single test in there
> that would test that ;-/
>
> chdir04 does check that name component is not too long, but that's
> a different codepath - it's individual filesystem's ->lookup() rejecting
> a component.
>
> Oh, well - not hard to add (to the same chdir04, for example)...

Crude variant on top of https://github.com/linux-test-project/ltp #master:

diff --git a/testcases/kernel/syscalls/chdir/chdir04.c b/testcases/kernel/syscalls/chdir/chdir04.c
index 6e53b7fef..7e959e090 100644
--- a/testcases/kernel/syscalls/chdir/chdir04.c
+++ b/testcases/kernel/syscalls/chdir/chdir04.c
@@ -11,6 +11,8 @@
#include "tst_test.h"

static char long_dir[] = "abcdefghijklmnopqrstmnopqrstuvwxyzabcdefghijklmnopqrstmnopqrstuvwxyzabcdefghijklmnopqrstmnopqrstuvwxyzabcdefghijklmnopqrstmnopqrstuvwxyzabcdefghijklmnopqrstmnopqrstuvwxyzabcdefghijklmnopqrstmnopqrstuvwxyzabcdefghijklmnopqrstmnopqrstuvwxyzabcdefghijklmnopqrstmnopqrstuvwxyz";
+static char long_path_4096[4096+1];
+static char long_path_4094[4094+1];
static char noexist_dir[] = "noexistdir";

static struct tcase {
@@ -20,16 +22,26 @@ static struct tcase {
{long_dir, ENAMETOOLONG},
{noexist_dir, ENOENT},
{0, EFAULT}, // bad_addr
+ {long_path_4096, ENAMETOOLONG},
+ {long_path_4094, 0},
};

static void verify_chdir(unsigned int i)
{
- TST_EXP_FAIL(chdir(tcases[i].dir), tcases[i].exp_errno, "chdir()");
+ if (tcases[i].exp_errno)
+ TST_EXP_FAIL(chdir(tcases[i].dir), tcases[i].exp_errno, "chdir()");
+ else
+ TST_EXP_PASS(chdir(tcases[i].dir), "chdir()");
}

static void setup(void)
{
tcases[2].dir = tst_get_bad_addr(NULL);
+ for (int i = 0; i < 4096; ) {
+ long_path_4096[i++] = '.';
+ long_path_4096[i++] = '/';
+ }
+ memcpy(long_path_4094, long_path_4096, 4094);
}

static struct tst_test test = {